This invention relates to a joy stick for electrically remote-controlling an oil pressure controlling valve used for oil pressure shovels or the like.
In a conventional joy stick, as shown in FIGS. 5 to 7, a box-like frame 3 is fitted below a fitting plate 2 for an operating lever 1, horizontal shafts 4 and 5 are rotatably borne in coaxial positions in a pair of side plates 3a and 3b opposed to each other of the frame 3 and a U-like connecting stripe piece 6 is secured inside both horizontal shafts 4 and 5. A sector gear 7 is secured to the outside part of one horizontal shaft and is meshed with a gear 10 fitted to a shaft 9 of a rotary potentiometer 8. As understood from FIG. 6, the same structure is fitted to a pair of side plates 3c and 3d in the direction at right angles.
The operating lever 1 is inserted and engaged at the tip in slots 11 provided in U-like stripe pieces 6 intersecting at right angles with each other so that, when the operating lever 1 is rotated and operated forward, rearward, rightward or leftward with a fulcrum A as a center, the shaft 9 of the rotary potentiometer 8 will rotate through the U-like stripe 6, horizontal shaft 4 and sector gear 7 and the contact position of the slider with a resistance line will be displaced to vary the resistance value.
In the formation of the rotary potentiometer 8, as shown in FIG. 7, for example, +10 volts and -10 volts are applied respectively to both terminals e and d so that, when the slider a is in the neutral position, the output may be a zero voltage. One rotary potentiometer 8 outputs from the output terminal b a voltage corresponding to the forward and rearward movements of the operating lever 1 and the other rotary potentiometer 8 outputs from the output terminal b a voltage corresponding to the rightward and leftward movements of the operating lever 1.
However, the potentiometer 8 has a fundamental defect that, as the slider a slides on a resistance line c, the resistance line c will be likely to be broken by the wear or the like.
Also, in using such a method as in the above mentioned conventional art wherein two potentiometers 8 issur signals instructing the movements in the four forward, rearward, rightward and leftward directions, even if the resistance line c is broken in any position, an applied voltage of +10 volts or -10 volts will be always output, therefore a finally controlled oil pressure actuator will become abnormal in the operation and a dangerous situation will be likely to occur.
The rotary potentiometer 8 to be fitted to the frame 3 must be adjusted so that its output may be a zero voltage when the operating lever is in the neutral position but there is a defect that, as the sector gear 7 is meshed with the gear 10 on the rotary potentiometer 8 side, the fitting work is complicated.